الفهرس 
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Abstract
The pineal gland is considered as a major ”neuroendocrine transducer”, as it converts a neural input into hormonal output with specific effects on reproduction, circadian organization, human mood, and sleeping habitat. Recent literatures illustrated the inhibitory effect of the Pineal gland hormone M. on growth of hormonal dependent cancers. M. concentration and the timing of M. administration seem to be crucial for arresting tumor growth. The present study aimed to assess the signaling pathways and mechanism of actions that are involved in melatonin inhibition of cancer cell growth, survival and metastasis using an in vivo model of Ehrlich solid tumors. The size of solid tumors of each group were measured twice weekly for one month. At the end of experiment, overnight fasted mice were anaesthetized with ketamine and xylazine (1:1), then blood and tumor samples were collected and stored preferably in liquid nitrogen till use. For histopathological and immunohistochemical studies, tumor samples were kept in 10% formalin till further processing.pathway using immunohistochemistry approaches. The presented data illustrated a significant effect of melatonin on up-regulating the expression of P53 which in turn up-regulated the expression of Bax and down-regulated Bcl2 expression as downstream targets of its signalling pathway of cell apoptosis. Interestingly, M. treatment showed a multi targeting effect of cancer cell apoptosis which indicated by the marked down-regulation at the expression of SVV which a member of anti-apoptotic IAP-family that Significantly up-regulated in resistant cancer cells for conventional therapy. These data were further confirmed by the induction at DNA fragmentation index in M. treated groups compared to E. and E+O groups which showed a marked tailed DNA. 7- The inhibitory effect of M. supplementation on cancer cell migration indicated by immunohistochemical localization of cancer cell motility promoting protein CD44 which is down-regulated in presence of M. as CD44 expression would lead to an up-regulation of MMP2 which would lead to extracellular matrix degradation. 8- Cancer cell metastasis would not have accomplished unless neo-angiogenesis carried out by overexpression of VEGF to initiate new blood vessels formation. This process is carried out under control of several molecules including CD44 which signals for VEGF expression via CD44/MMPs/CD146s/ VEGF signalling pathway. Conclusion: Melatonin has a remarkable effect on inhibition of Ehrlich cells growth survival and metastasis. This occurs through the M. dependent down-regulation of Ox. Stress, leading to miRNA-96 reduction which in turn up-regulated FoxO1 transcription factor leading to E. cells death via P53-depndent pathway which was confirmed by DNA fragmentation. The ability of E. cell to metastasis was markedly diminished via down-regulating CD44/MMP2/VEGF expressions. M. inhibited cancer cell proliferation which was indicated by the reduction at tumor size, cell cycle arrest at G0/G1 phase and diminishment of Ki67 expression. M. treated tumors were significantly diminished in size with marked presence of necrotic and apoptotic cells with isolated islands of few E. cells with signs of fragmented nuclei. The main outcomes from this study developed data may be concise in the followings; 1- In the present study, the quality of surgical destruction of the pineal gland to diminish M. secretion was confirmed by brain staining with Alizarin blue, M. down-regulation in blood plasma of operated groups. Exogenous supplementation of M. (20 mg ⁄kg) significantly restored the level of plasma melatonin in operated mice. 2- Carcinogenic effect of M. reduction was confirmed first, by the increase at solid tumors size in absence of melatonin and the reduction at their size with M. supplementation which is confirmed by histopathological data. Second, reduction of M. led to a significant up-regulation at breast cancer prognostic markers CEA, TNFα, NFƘβ and miRNA-215 in blood plasma. These effects were significantly overcoming by exogenous M. supplementation. 3- The inhibitory effect of M. on cancer cell proliferation was indicated by flow cytometric analyses of the tumor cell cycle, revealed a significant effect of M. treatment on inducing cell cycle arrest at G0⁄G1 phase. These data were further confirmed by the significant downregulation at cell proliferation marker Ki67 along with M. supplementation compared to E. and E+O groups. 4- An expected elevation at the level of oxidative stress, were significantly recorded at MDA, H2O2, and NO levels in E+O, E., and, O groups, respectively. M. supplementation, significantly downregulated the level of oxidative stress. 5- The effect of exogenous M. on Oxidative stress directs our attention to investigate the expression of FoxO1, which is a transcription factor signalling for cancer cell apoptosis and strongly affected by the level of oxidative stress. Supplementation of M. significantly up-regulated FoxO1 transcriptional levels in tumor cells compared to E. and E+O. groups. For further analyses of M. signalling cascade to induce cancer cell apoptosis via up-regulating FoxO1 expression was conducted by assessing the expression of miRNA-96 which is an oncogenic miRNA implicated in regulation of FoxO1 expression. The data confirmed the role of M. supplementation on downregulating miRNA-96 expression in comparison with E. and E+O. groups.